Studies on carcinoembryonic antigen (CEA) included the antigen of human, rat and murine origin. The enzyme-linked immunosorbent assay (ELISA) was developed to detect human CEA, which has sensitivity of 100 ng/ml and which is being employed for detection of CEA in human feces. Study on tissue specificity led to the description of thermostable ethanol insoluble antigens characteristic for pancreas of ox and man. The human antigen was obtained in purified form as a protein of 68,000 daltons. The excretion of pancreas-specific antigen to the duodenum by patients with pancreatic carcinoma is under investigation. Studies on heterophile antigens were mostly devoted to the analysis of Paul-Bunnell (P-B) antigenic specificities. Two components of the P-B antigenic complex could be clearly defined, the BS component shared by sheep and ox, and the B component present in ox but not in sheep. The appearance of these two components in buffy coat and in the circulation of patients with infectious mononucleosis and other diseases was studied. The results suggested that serologically negative cases of infectious mononucleosis may be due to excessive production and release of the P-B antigens. Interestingly, the B but not BS antigen could be demonstrated frequently in pathological human sera; 30% of lymphoma-leukemia sera, 15% of carcinoma sera, and 10% of SLE sera.